1. Field of the Invention
Embodiments of the present invention generally relate to the removal and reduction of electrochemically evolved gases in electroplating and electropolishing systems.
2. Description of the Related Art
Metallization for sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. In devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio interconnect features with a conductive material, such as copper or aluminum. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) have been used to fill these interconnect features. However, as interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result thereof, plating techniques, such as electrochemical plating (ECP) and electroless plating, for example, have emerged as viable processes for filling sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.
In an ECP process sub-quarter micron sized high aspect ratio features formed on a substrate surface may be efficiently filled with a conductive material, such as copper. ECP plating processes are generally two stage processes, wherein a seed layer is first formed over the surface features of the substrate, and then the surface features of the substrate are exposed to an electrolyte solution while an electrical bias is simultaneously applied between the substrate and an anode positioned within the electrolyte solution. The electrolyte solution is generally rich in ions to be plated onto the surface of the substrate. Therefore, the application of the electrical bias causes these ions to be urged out of the electrolyte solution and to be plated as a metal on the seed layer. The plated metal, which may be copper, for example, grows in thickness and forms a copper layer that fills the features formed on the substrate surface.
In order to facilitate and control this plating process, several additives may be utilized in the electrolyte plating solution. For example, a typical electrolyte solution used for copper electroplating may consist of copper sulfate solution, which provides the copper to be plated, having sulfuric acid and copper chloride added thereto. The sulfuric acid may generally operate to modify the acidity and conductivity of the solution. The electrolytic solutions also generally contain various organic molecules, which may be accelerators, suppressors, levelers, brighteners, etc. These organic molecules are generally added to the plating solution in order to facilitate void-free super-fill of high aspect ratio features and planarized copper deposition.
Furthermore, conventional systems may utilize a soluble metal anode to provide a continuous supply of metal ions for electrolyte replenishment. However, anode dissolution has disadvantages such as undesirable side products, e.g., sludge and copper ball formation, and undesirable side effects, e.g., anode passivation, non-uniform anode dissolution, and consumption/breakdown of organic additives. Therefore, an insoluble anode may be utilized in electrochemical plating systems. However, the electrical bias applied to the anode may cause oxygen to form, thereby saturating the plating solution with oxygen and oxygen bubbles. Occasionally, when the pulse current or reverse current is applied for electroplating, both oxygen and hydrogen bubbles are formed. Oxygen and hydrogen bubbles may cause undesirable side effects, such as non-uniformity of the copper deposit distribution, formation of bubbles on the substrate, and blockage of the anode and membranes present in the plating cell. Therefore, there is a need for a method and apparatus that minimize the formation and effects of oxygen in semiconductor electroplating baths, wherein the method and apparatus addresses the deficiencies of conventional devices.